Recent investigations into glutamate receptor function have identified important roles for these receptors in regulating the function of the hippocampus, a primary site of pathology in certain neurological disorders such as Alzheimer's disease and temporal lobe epilepsy. The studies outlined in this proposal will help to elucidate the mechanisms that regulate the function of glutamate receptors and therefore lead to a clearer understanding of hippocampal function. The purpose of these studies is to determine the role that G-protein-coupled receptor kinase 2 (GRK2) plays in regulating the function of metabotropic glutamate receptor 5 (mGluR5). The following specific aims will be tested. Specific aim 1 is to test the hypothesis that mGluR5 undergoes GRK2-dependent phosphorylation and desensitization. The effect of GRK2 overexpression on mGluR5 coupling to inward-rectifier potassium channels, phosphoinositide hydrolysis, and release of Ca2+ from intracellular stores will be determined. The desensitization of these responses and the phosphorylation of mGluR5 will be monitored. Specific aim 2 is to identify the specific phosporylation sites on mGluR5 that are responsible for GRK2-mediated desensitization. The desensitization and phosphorylation of mutant mGluR5 in which specific phosphorylation sites have been mutated will be determined. Specific aim 3 is to determine the effect of GRK2 inhibition on mGluR5 signaling in hippocampal slices. Peptide inhibitors of GRK2 and functional GRK2 antibodies will be applied to hippocampal pyramidal cells through a patch pipette and the desensitization of mGluR5-mediated current recordings upon repeated application of agonist will be monitored.